I have a simple normally open push button switch for HOME on the X axis. I have wired it up and it does read correctly in the "DIAGNOSTICS" screen.
But: I can't get Mach3 to actually zero out on the switch. Try jogging it manually and pressing the switch, it doesn't react.
If I setup the switch as limit also, the machine does stop but still doesn't zero out the X axis.

You need to press RefAll button to initiate the nhoming. The axis that you have configured will move to the switch, back off until switch closes and assuming you have Auto Zero set in homing and limits it will zero the machine coords. Note it is the machine coords that get zeroed, that may not be the same as your work offsets, all depends how you have things set up.
Hood